It’s all about SCoP

It’s all about the SCoP

When selecting a heat pump a more accurate and useful characteristic of operational performance is the seasonally adjusted annual average efficiency measure, says Adrian Walker

Adrian Walker

National sales manager at Strebel Heating Technology

www.strebel.co.uk

ou makes your choice. You

Ypays your money.” This phrase comes to mind when I talk to design consultants and building owners about selecting from the range of commercial heating products that are on offer today.

Aside from the clear direction towards electricity as the input ‘fuel’ for space heating, by which I mean the seemingly irrepressible drive to select air source heat pumps over gas boilers for almost every application, there is also a wide range of considerations when selecting a heat pump.

Unlike modern condensing gas boilers which generally share similar operating efficiency performances (around 95 per cent Part L Seasonal Efficiency) and output temperatures (generally up to around 90oC) it is a totally different picture when it comes to the published efficiencies of available air source heat pumps. Essentially all these machines operate in the same way by transferring heat from a compressed refrigerant into a wet system across a plate heat exchanger. However, there is a wide variation in how efficiently this happens and, as a result, a wide variation in the running costs of different machines on the market.

Forefront of product design

At Strebel we have always taken the view that highly efficient heating technology should be at the forefront of product design. There are always going to be different manufactured goods on the market, each with their own idiosyncrasies, but fundamentally one performance characteristic stands out to us when we consider bringing a product to market – that it operates with a low cost and delivers the required amount of useful heat at the required temperature. This has never been more pertinent than today with the elevated cost of energy; specifically with the drive towards the electrification of heat with its significantly higher kWh cost compared to natural gas.

With the recent revisions of the Building Regulations driving a reduction in system operating temperatures down to a maximum of 55C there is a clear direction towards the application of air source heat pumps as these operate with a higher Coefficient of Performance (CoP) at lower flow temperatures. However, a more accurate and useful characteristic of operational performance is the seasonally adjusted annual average efficiency measure. In the case of air source heat pumps this is the Seasonal Coefficient of Performance (SCoP) value. Simply put the higher the SCoP of the machine the less energy it will use, and therefore the lower the electricity bill will be.

Correctly sized fans

Product design engineers have several ways to achieve high SCoP when designing heat pumps. Surface area and air gap spacing in heat exchanger design are critical, as is selection of correctly sized fans. Paramount, however, is the matching of compressors with a refrigerant to optimise both thermal power and temperature in the most efficient manner.

Different refrigerants, dependant on their density and composition, possess different thermal conductivity characteristics when matched with compressors to offer a wide range of temperature outputs and thermal efficiencies.

Clearly, all building operators will favour design changes that encourage an improvement in efficiency as this will drive down running costs. With energy costs front and central for the foreseeable future

The higher the SCoP of the heat pump the less energy it will consume

installing technology that reduces running costs is the fundamental challenge for designers of air source heat pumps which, let us not forget, cost significantly more than modern gas boilers to buy, and run on an energy source, electricity, that is also between three and four times more expensive than natural gas per kWh.

Highest SCoP performance

Therefore, when selecting an air source heat pump we consider the golden rule is to select the machine that gives the highest SCoP performance at the output and temperature required for each project. After all machines that use less energy not only cost less to run but also, by definition, have a lower operational emissions footprint by the fact they use less energy in the first place.

If the project requires a higher than usual temperature – say up to 68C for a retrofit installation – then it is key to consider the SCoP at a high temperature. Our S-ASX-VP machine, with a SCoP of 3.09 at 65ºC has been designed for just such applications combining twin scroll compressors with an additional vapour and liquid injection system and a R410A

The seasonally adjusted annual average efficiency measure is a more accurate characteristic of operational performance

refrigerant circuit.

Alternatively, if the project has been designed to operate at a lower temperature – say up to 55ºC for a new build – then it is more appropriate to consider the SCoP at that level. Our S-ASX-LP model, with a SCoP of 3.37 at 55ºC, is the optimal selection matching twin scroll compressors with a low GWP R454B refrigerant in this case.

As SCoP outputs and achievable consistent outlet temperatures vary with different compressor and refrigerant combinations so, of course, do the GWP ratings of the chosen refrigerants as well as the embodied carbon numbers for each machine. Making all such information accessible and easy to read is a key responsibility of the manufacturer. Publication of TM65 data as well as full performance characteristics in terms of thermal output and CoP at different Air and Water temperatures is critical. Clearly having SCoP data available at different system flow temperatures will also assist optimal machine selection. ■

Heat pumps recognised for top design

The Aquarea K and L Generation heat pumps have been recognised in the 2022 Good Design Awards (sponsored by the Japan Institute of Design Promotion). As well as recognising the performance efficiencies of the units, the judges commended the outdoor unit’s design contributes to the improvement of the surrounding environment.

The Good Design Award selects “good design” from various industries and an experienced jury panel deliberates to recognise design that aims to lead our lives, industries, and society as a whole to

This year’s award scheme received 5,715 entries, with a total of 1,560 submissions being selected for awards. Among all the winners, 100 designs received especially high evaluations from jury members and were selected as the GOOD DESIGN BEST100, including Panasonic’s Aquarea K & L Generation Heat Pumps.

Available from Spring 2023, the new models are focused on improving energy performance and offer a series utilising a natural refrigerant: Aquarea K Generation: uses R32 refrigerant and is ideal for heating, cooling and domestic hot water production that delivers outstanding performance, even at extreme outdoor temperatures. This model is particularly suitable for new installations and wellinsulated homes. T-CAP available. Aquarea L Generation: using the natural refrigerant R290, L generation models have a hydraulic connection between the indoor and outdoor unit, providing water outlet temperatures of up to 75°C down to -10°C. These units are ideal for retrofit applications, when renovating a home with existing radiators.

In securing a place in the 2022 Good Design Awards, the judges commented that Panasonic’s design for the Aquarea K & L Generation “has been raised to an appearance that blends into the landscape and contributes to the improvement of the surrounding environment. "In addition, considering the fact that many remote-control devices are mixed on the wall, the remote control adopts a flexible system that can be installed either integrally with the indoor hot water tank or separately.”